Process for stabilization of copper treated oils



Patented May 20, 1941' PROCESS FOR STABILIZATION OF COPPER TREATED OILSWalter A. Schulze, Bartlesville, 0kla., and Graham H.. Short, Phillips,Tex., assignors to Phillips Petroleum Company, a corporation of DelawareNo Drawing. Original application November 9, 1938, Serial No. 239,731.Divided and this application May 28, 1940, Serial No. 337,736

2 Claims.

This invention relates to a new and useful process for treatinghydrocarbon oil. More specifically, this invention relates to a processfor stabilizing or preventing the deterioration of hydrocarbon oil whichhas undergone a purifymg treatment with reagents containing copper.

This application is a division of our copending application SerialNumber 239,731, filed November 9, 1938.

Hydrocarbon oil, particularly petroleum distillates usually containimpurities, including sulfur compounds, whichcause the oil to exhibitundesirable properties such as bad odor and gum and color formation- Itis customary, therefore, to subject said impure oil to a purifyingtreatment in order to remove the impurities or to convert them to lessobjectionable forms, for example, the conversion of mercaptans todisulfides.

The methods of treatment for the removal or conversion of mercaptansmake use of various chemical processes, and of these processes, one ofthe most satisfactory is the process utilizing copper, salts of copper,or solutions containing copper salts.

\ However, subsequent to. treatment with coppercontaining reagents, ithas been found that many hydrocarbon oils require further treatment 01'stabilization. This condition is due to the fact that said unstable oilsretain from their contact with copper reagents, extremely smallquantities of oil-soluble copper compounds. These traces of coppercompounds remaining in the oil are responsible for the markedacceleration of reactions which lead to the formation in said oil ofcolor, gum, resinous deposits and polymers; these deteriorative changesseriously impair such properties of the oil as color, gum content andoctane number.

One object of this invention is to effect the removal of traces ofcopper compounds from hydrocarbon oils.

Another object of this invention is to prevent the deterioration ofhydrocarbon oil which has been treated with copper reagents by theremoval from said oil of small amounts of retained oilsolublecoppercompounds responsible for aforesaid deterioration.

A further object of this invention is the production of hydrocarbon oilof good color and stable with respect to gum formation subsequent totreatment with copper-containing reagents.

A further object of this invention is the treatment of oil which retainstraces of copper compounds subsequent to sweetening with copperreagents, to remove said copper from the oil,

thereby delaying or preventing deterioration.

Another object of this'invention is to provide a step in the sweeteningof hydrocarbon oil with copper reagents whereby the sweetened oil isstabilized against deterioration by the removal therefrom of retainedcopper salts.

Another object of this invention is the converand/or formation ofresinous matter, polymers and oxidation products; that is, a method ofstabilizing the oil by bringing it in contact with an alkaline sulphidesolution subsequent to treating with the copper reagent.

We have now discovered that copper treated oils may be stabilized bymeans other than the alkaline sulfide solution referred to above andcaptide, the next number in the series,

more soluble, yet its actual solubility figure isthat these meansinvolve certain improvements and advantages. This discovery is extremelyimportant in that it clearly defines the conditions which must be met toproduce stabilizedoils. This discovery, likewise makes it possible todivide treating agents into two groups, the first group consisting ofthose reagents which will effectively remove the hydrocarbon oil-solublecopper compounds and thereby stabilize the oil, and the second groupconsisting of those reagents which will not remove suflicient quantitiesof the copper compounds to stabilize the oil.

We have found that copper mercaptides increase in solubility in the oilwith increasing molecular weight of the mercaptans. Copper methylmercaptide is the most insoluble of all the copper mercaptides and isalmost totally insoluble in hydrocarbon oils. Copper ethyl meris alittle extremely lowa Copper butyl mercaptides and amyl mercaptides aremuch more soluble and their solubilities may be determined in the usualmanner of precise measurements.

We have now discovered that hydrocarbon oil' containing copper methylmercaptide, and therefore completely saturated with respect tothesubstancadoes not showany of the undesirable reactions mentioned aboveas resulting from the catalytic effect of dissolved copper compounds. Inother'words, we have established that the con soluble copper methylcentration of copper from a saturated solution of copper methylmercaptide in hydrocarbon oil is too low to cause deterioration of theoils. On the other hand, we have found that if the hydrocarbon issaturated with'respect to copper ethyl mercaptide, the concentration ofcopper is just suflicient to cause a slow depreciation in the saidproperties of the oil. Thus, we have established that there is acritical value for copper concentration in the oil, above whichdeterioration will occur, and below which the oil will be .stable asregards gum and color formation in storage- This improved process ofstabilization depends on the efiective removal of traces of coppercompounds from the contaminated hydrocarbon oil by treating said oil tocompletely convert the hydrocarbon oil-soluble copper compounds intocompounds whose solubility is less than the solubility of the coppersalt of ethyl mercaptan. By this means, and the subsequent separation ofthese more insoluble compounds from the hydrocarbon oil, thedeterioration due to dissolved copper compounds in the oil is prevented.Since the deterioration of oil is accelerated in a catalytic manner bydissolved copper salts, it follows that copper salts more insoluble thancopper ethyl mercaptide are inactive ascatalysts for deteriorativereactions in oil, and likewise possess marked resistance to oxidatingprocesses phosphate solutions, or by the addition to the oil ofcontrolled amounts of ethyl mercaptan.

In order to explain more exactly the criterion by which thestabilization of copper-containin oil is Judged, the relativesolubilities of the copper compounds encountered may be' considered.

The sulfides of copper are the most insoluble compounds of the metal.The mercaptides by reason of analogous structure exhibit similarsolubilities in water, but are slightly more soluble in oils dueto theorganic nature of the alkyl or .aryl group present in the mercaptidemolecule.

The sulfides of copper have a solubility of about 0.00033- gram perliter of water and an inflnitesimal solubility in hydrocarbon oils; thesolubility of copper methyl mercaptideis approximately 0.000003 gram perliter of cracked naphtha, or about one-hundredth the solubility ofcopper sulfide in water. These solubility figures are based on extremelysensitive colorimetric tests, especially devised to indicate thepresence and concentration of copper in hydrocarbon oil. A

The following table shows the approximate solubilities of copper saltsin oils, or the extent to which oil-soluble copper compounds are formedby contact of the oils with said copper salts for a 24 hour period.

Table I v b 0 Copper salt Hydrocarbon oil g f COD 9 ggg gi g PcrjaperGrams per 1000 cc. million of oil Copper oxide Doctor-sweet crackednaphtha. 0.0003 Sapprox.) Copper carbonate (basic) ..d0 0.0003 approx.)Copper bydroxide 0.0003 (approx.) Copper phosphate 0.0003 (approx.)Copper cyanide (KCN so 0.0003 (approx) Copper silicate 0.0003 (approx.)Copper sulflte 0.0003 (approx.) Copper-n-butyl-mercuptide- 0.0003(approx) Copper-t-butyl-mercaptidc. 0.300 Copper-ethyl-mercaptide0.00003 1 Sp. gr. oi naphtha taken as 0.75.

which would change said insoluble copper compounds to more active formswhich would be injurious to the oil.

Oil-soluble copper compounds which may be formed in complex hydrocarbon-oil mixtures, particularly in petroleum distillates, are usuallymercaptides or salts of acidic components such as cresylic andnaphthenic acids: Such compounds may be more soluble than copper ethylmercaptide, and likewise may not be removed from an oil in which saidcompounds are dis-, solved unless the method of treating orstabilization forms therewith copper compounds less soluble than copperethyl mercaptide. For example, after a cracked naphtha has been in con-itact with copper oxide, copper carbonate or copper phosphate, sensitivetests show the presence of traces of copper remaining in the naphtha,whereas a portion of the same naphtha after prolonged contact withcopper methyl mercaptide shows no evidence of dissolved coppercompounds. Further, the small amounts of copper saltspresent in acracked gasoline which has been sweetened with a cupric chloridesolution may be removed by adding thereto a controlled amount of methylmercaptan to convert the more soluble copper compounds into the lessmercaptide. Complete is not effected by treattic soda, carbonate orremoval of the copper ment of the oil with caus It will be seen from thevalues listed in Table I that complete removal of copper from an oil maynot be accompli with a reagent to form any of the copper salts listed.This fact is based on experimental data which proves that thedeterioration of an oil due to dissolved copper is not prevented unlessthe copper content of said oil is reduced to a value less than 0.1 p. p.m. as shown in Table II.

Thusin order to prevent the deterioration of a hydrocarbon oil which hasbeen treated with a copper-containing reagent, it is necessary to treatsaid oil in order to reduce the amount of dissolved copper to a valueless than 0.1 p. p. m.

This is accomplished according .to our invention by converting thecopper present in the oil into shed by contacting said oil compoundswith oil solubility less than the oilsolubility of copper-ethylmercaptide.

As examples of the practice of my invention, the following examples aredescribed:

EXAMPLE I A sample of cracked gasoline which had been sweetened bytreatment with a solution containing cupric chloride was separated fromthe copper reagent and divided into two parts. One part was storedwithout further treatment. To the other portion was added a solution ofmethyl mercaptan in sulfur-free hexane solution, the quantity addedbeing sufficient to cause the gas- EXAMPLE III To a sample of doctorsweet cracked gasoline was added solid copper ethyl mercaptide and 5shaken until the oil was saturated with the oline to have a methylmercaptan content of 15 given below:

Table III v Color Color No. Gasoline sample Copper test inal tig astercolor y storage storage 1 Cracked gasoline-no additional treatmentNegative +24 +22 +21 2 Crtagked gasoline-saturated with solidcopper-ethyl-mercap- Positive, approx. +24 +16 i e. 1 p. p. m. I 3 #2sample-added 0.000 per cent methyl mercaptan followed Negative, less +24+22 +21 by water wash. than 0.1 p. p. m. 4 #2 sample-plus 2 per centsour vapor recovery gasoline com +24 +21 mining 0.01 per cent methylmercaptan. 5 #2tsampefiihntimately contacted with alkaline aqueous solu+24 +22 +21 ion 0 l izone. 6 #2 sample-contacted with arnmoniacalsolution of alpha- +24 +22 +21 benzoinoxime. #2 sample-contacted withaqueous solution of thional de. +24 +22 +21 #2 sample-contacted withaqueous solution of 6.7-d1bromo- +24 +22 +21 hydroxyquinoline. #2sample-contacted with ammonlacal solution of diethyldi- +24 +22 +21thiocarbonate.

0.003 weight per cent. After the addition of the mercaptan, the gasolinewas allowed to stand in which deterioration is' for two hours, afterwhich it was washed with water and stored. The results of thisstabilizing treatment are shown below:

These samples are illustrative of the manner preventedin hydrocarbonoils containing soluble copper compounds,

according to the practice of this invention and the critical value forallowable copper concen-- Orig" 9 A aft 30 er ppesrance er Gasolinesamples Copper test cigfir days, days, storage I storage Crackedgasoline unstsbilized Positive, greater than 1 p. p. m.--. +24 --16 Darkbrown, gummy. Cracked gasoline plus 0.003 perv cent Negative, less than0.1 p. p. m +24 +23 +22 color.

methylmercaptan.

1 This gasoline was doctor sweet; no trace of mereoptan after two days.

EXAMPLEII tration in oil which is stable with regard to color A sampleof the same gasoline described in and gumformartionm storage is thusdisclosed Example I was similarly treated except that the stabilizingreaction was brought about by the addition to one portion of thegasoline of sufficient sour vapor recovery gasoline to amount to 2 percent by volume. This vapor recovery gasoline contained approximately .01weight per cent of methyl mercaptan. -The results of this stabilizationare illustrated below:

We claim:

1. In the process of sweetening hydrocarbon oil with copper reagents,the step of stabilizing the sweetened oil to prevent deterioration-dueto retained oil .soluble copper salts which comprises adding a smallquantity of a stabilizing agent comprising 5.7-dibromohydroxyquinoline.

2. The process in claim 1 in which the stabiliz Ori A rance Gasolinesample Copper test m5 fig are???) days color storage storage 'Creckedgasoline-copper treated-unstabilized. Positive greater than 0.1 p. p. m24 '-16' Darkb wn. Cracked gmoline-copper treated plus 2 per centNegative, less than 0.1 p. p. m.... :24 +23 +22 cob a.

(vol.) of sour vapor recovery gasoline.

1 This gasoline was doctor sweet.

ing agent is an aqueous solution of 5.7-dibromo-

